OK that makes more sense. We did the exact same cruise. :-) You will go though immigration in Hobart but when you collect your bags in Sydney you will have to go through customs - its pretty much a formality. We just walked straight through with you bags. They line all the bags up in the building near the dock and you collect them when your colour is called. You then just go to the airport with your bags that day as normal and then fly up to Cairns. We caught the train from circular key but it was quite expensive. It costs around the same for a cab apparently. After you check your bags in you can catch a train back into the city for some quick site seeing. :-) Mummsie